The invention is directed to an apparatus for transferring a high voltage to the ignition elements of an internal combustion engine. The apparatus comprises first and second units which form spark discharge gaps, the high voltage being provided to one of the electrode units and the other electrode unit being connected to the ignition elements of the internal combustion engine.
In order to ignite a gas-air mixture in a cylinder of an internal combustion engine, a high voltage is transferred to an ignition element provided in the cylinder. The cylinders are selected according to the firing order by means of a flash-over distributor. In order to do this, the high voltage generated in a high voltage generating device at the firing point is supplied to a distributor rotor. At the point of ignition of the cylinder, a first electrode unit provided at the rotor is positioned opposite a second electrode unit, which is connected to the ignition element provided in the cylinder via a connecting line, said cylinder containing the inflammable gas-air mixture. Therefore, at the firing point, the first electrode unit of the rotor and the second electrode unit form a spark discharge gap, which is placed in series with the spark discharge gap of the ignition element, for example, the electrodes of a spark plug. The high voltage generated in the high voltage generating device at the firing point flashes over from the first electrode unit to the second electrode unit and between the electrodes of the plug so that the inflammable gas-air mixture is ignited.
The high voltage generating device which always generates the high voltage necessary for the ignition only at the respective firing point, mostly consists of an ignition coil (SZ) comprising an autotransformer, whose first primary winding is connected to an interruptor and whose second primary winding is connected to the line voltage of the automobile. If the interruptor, which mostly is also accommodated in the distributor, is closed, a magnetic field is created due to the current flow through the primary coil. At the firing point, the interruptor is opened and a high voltage is produced at the secondary winding of the ignition coil. The thus produced high voltage is supplied from the secondary winding of the ignition coil to the first electrode unit of the rotor in the distributor. Without mentioning the numerous losses, the magnetic energy stored in the primary winding is substantially supplied to the respective ignition element, said magnetic energy being calculated according to the formula EQU W.sub.L =1/2Li.sup.2
("L" corresponds to the inductivity, "i" corresponds to the current, which flows through the primary winding at the firing point and is interrupted.)
The high voltage generation by means of the coil ignition produces a spark at the electrodes of the plug, said spark having a long burning time, and the coil ignition is quite cheap so that it is mostly used in small and in middle class cars. However, besides the advantages, said coil ignition also has considerable disadvantages, as e.g., that the contacts of the interruptor burn up, that the mechanical operating devices of the interruptor get worn out, and that the amplitude of the high voltage decreases in intensity with an increased rotational speed of the motor and thus with the generation frequency. In order to eliminate a part of the numerous disadvantages of the coil ignition, a transistor-coil ignition (TSZ) was proposed as a further development. There, the interruptor is replaced by a transistor, whereby the break contact is relieved and need not be substituted so soon.
On the one hand, the transistor-coil ignition eliminates disadvantages of the coil ignition (SZ) but, on the other hand, causes disadvantages, as e.g., temperature dependence problems, and does not eliminate all disadvantages.
Therefore, on the basis of the coil ignition and the transistor-coil ignition, the capacitor ignition (HKZ) was proposed as a further development. The difference between the capacitor ignition and the aforementioned ignitions SZ, TSZ is that the necessary ignition energy--leaving losses apart--is not longer stored in a coil but in a capacitor. Thus, the ignition energy is in relation with the energy stored in the capacitor, which can be determined by the formula EQU W.sub.C =1/2Cu.sup.2
("C" corresponds to the capacity of the capacitor, "u" corresponds to the voltage, with which the capacitor is charged up to the ignition time point.)
At the ignition time point, the capacitor is mostly discharged via a thyristor. The discharging current of the capacitor flows through the primary winding of a transformer, at the secondary side of which a high voltage pulse is produced, which is supplied to the respective ignition element via a first electrode unit of the rotor. It is true that the capacitor ignition furnishes a high voltage pulse compared to the aforementioned ignitions, said high voltage pulse showing a steep increase, but, on the other hand, the burning time of the high voltage pulse is very low compared to the other ignitions. Therefore, numerous mixed form of the mentioned ignitions SZ, TSZ and HKZ were further proposed. Furthermore, it was proposed--due to the above-mentioned difficulties and other difficulties--to use so-called "contactless interruptors", as e.g., hall probes, field plates, optical sensors, etc.
Despite developing attempts lasting for decades it has not been possible, by using one of the mentioned ignitions SZ, TSZ, HKZ and a mixed form thereof, to solve the problem of the emission of noxious substances, like nitrogen oxide and hydrocarbon, tightly connected with the ignition. In order to reduce the emission of noxious substances and the consumption of gasoline, it was thus proposed to acquire all operating data of the internal combustion engine, to process said data in a micro-processor system and to control one of the above-mentioned ignitions by means of this micro-processor system.
The disadvantage of the above-mentioned ignition systems is that they use a principle of high voltage generation, in which the required high voltage is always generated shortly before the firing point. As can be easily realized, it is difficult, especially when there are high rotational speeds, to generate a hundred times per minute an ignition pulse of sufficient intensity, of large steep rise times and with a long spark burning time and to bring the ignition pulse to coincidence with the optimum point of ignition, which is constantly varying. Should, in addition thereto, the emission of noxious substances be influenced via the ignition, this will inevitably lead to highly-sophisticated, electronic systems, if one of the above-mentioned ignitions is used, wherein the high voltage generation and the use thereof almost coincide. In this connection, those of the above-mentioned ignition systems which are useful to a certain extent, have a very large number of electronic components. Due to these high numbers of components and due to the required reliability--the probability of the failure does not show a linear rise with an increased number of components--the proposed ignition systems and the ignition systems to be expected, which build up on these known ignition systems, are too expensive, especially for small cars and middle class cars which, moreover, represent the majority of automobiles. Consequently, it will be difficult to reduce the emission of noxious substances, especially of hydrocarbons and nitrogen oxides, by means of one of the cited ignition systems using the principle of generating the high voltage each time shortly before its utilization.
As is explained above, the ignition energy is derived from the energy stored temporarily in a coil or a capacitor, whereby the energy in the coil or in the capacitor is obtained each time shortly before its utilization at the ignition time point, by creating magnetic or electric fields. Apart from the fact that this principle of high voltage generation--the point of time of the high voltage generation nearly coincides with the firing point--entails all difficulties of a transient process, and this kind of high voltage generation additionally shows a very bad efficiency; further, this kind of high voltage generation is not suited for influencing the emission of noxious substances via the ignition, as will be explained in the following.
In order to reduce the emission of noxious substances as nitrogen oxide and hydrocarbons, it is necessary to adjust the fuel-air mixture ratio in a direction to a larger air proportion, the so-called "lean concept". The fuel-air mixture is designated by and represents the ratio of an air mass acutally supplied for burning a fuel mass to the air mass theoretically required for a perfect combustion. In this connection, .lambda.&gt;1 corresponds to the combustion under excessive air (lean mixture) and .lambda.&lt;1 corresponds to the combustion under a fuel surplus (rich mixture). In internal combustion engines working according to the Otto-engine the air proportion .lambda. lies in the range of .lambda.=0.8 to 1.2. Further, it is known that with an air proportion of .lambda.=1.3 there exists a point of intersection between the curves of the noxious emission of hydrocarbon and the noxious emission of nitrogen oxide. With an air proportion larger than .lambda.=1.3, the emission of hydrocarbon increases and the nitrogen oxide content further decreases. Vice versa, the nitrogen oxide content increases with an air proportion .lambda.=1.3 and the emission of hydrocarbon slightly decreases.
For igniting a fuel-air mixture with a conventional ignition system--as described above--within the short period of time, in which the ignition pulse is applied to the electrodes of the plug, it is necessary that there exists an inflammable mixture when the spark flashes over between the electrodes of the plug. If the fuel-air mixture contains a larger air proportion .lambda. due to the lean concept, shifted more in direction to the probability in conventional ignition systems decreases that the ignition spark meets with an inflammable mixture within the short period of time of the flashing-over. If a coil is used for the energy temporary storage, the ignition spark has a sufficient burning time but the steep rise time of the high voltage pulse is missing, as is the case in the ignition system working according to the HKZ-principle, which uses a capacitor for temporarily storing the energy. Just when there is lean fuel-air mixture with a large air-proportion, it is necessary for inflamming the mixture that the high voltage pulse between the electrodes of the plug shows a steep rise in voltage and a sufficient burning time. In the conventional ignition systems as mentioned above both requirements can be fulfilled--if at all--only by means of a large expenditure of electronic components.
Furthermore, the above-mentioned conventional ignition systems have the disadvantage that at the ignition time point only a determined energy amount is provided. Part of this energy amount must be used to cover the losses in the ignition system, and moreover, part of the energy is lost due to the charging of parasitic capacities, which are formed through the lines, and furthermore, part of the energy demand must be used to ionize the spark discharger gaps and to create the plasma or spark discharger gap channel. Only the remaining part of the energy demand provided by the conventional ignition systems serves to inflame the gas mixture.
Moreover, in conventional ignition systems, it will be possible to fulfil the inflammation of unleaded fuel or of other fuels, by meeting the above requirements, only with an additionally larger expenditure of components.